Composite parts, such as those used in the manufacture of aircraft, can be constructed using various production methods, such as filament winding, tape placement, overbraid, chop fiber roving, coating, hand lay-up, or other composite processing techniques and curing processes. Most of these processes use a rigid cure tool/mandrel on which composite material is applied and then cured into a rigid composite part. For example, automated fiber placement (AFP) machines or other automated lamination equipment may be used to place fiber reinforcements on molds or mandrels to form composite layups. Following, composite parts may be cured within an autoclave that applies heat and pressure to the part during a cure cycle.
Some composite part geometries include internal cavities that may cause the part to collapse under application of composite material or autoclave pressure unless a tool such as a bladder or mandrel tool is placed in the cavity.
Many types of mandrel tools exist. One example type is a semi-rigid tool in which tooling is used that is not as stiff as is desirable at room temperature and/or not as flexible as desirable at elevated temperatures. Another example type is a fully-rigid tool in which tooling is used that is rigid through the entire fabrication process, however, the tooling may have limited ability to conform to the composite part so as to distribute pressure evenly during the curing process. Still other mandrel tools exist that include shape memory polymers (SMP). SMP materials allow rigid tooling at room temperature that becomes flexible at elevated temperatures, however, SMP's require an expensive secondary manufacturing step to reheat and reform (e.g., blow mold) the SMP's to an original rigid geometry after each use for re-use of the tool.
Accordingly, there is a need for a bladder design that will allow the bladder to be rigid during automated lamination that will also allow the bladder to be flexible during the curing cycle.